A Co9S8-Ni3S2 / NCF self-reconstructs into Ni x Co 3-x O4-Ov-SO4 2- Method for enhancing the activity and stability of oxygen evolution reaction by using NCF

Abstract

The present invention discloses a method for self-reconstruction of Co9S8-Ni3S2 / NCF into Ni x Co 3‑x O4‑Ov‑SO4 2‑ / NCF enhances the activity and stability of oxygen evolution reaction, and adopts the self-reconstruction strategy of Co9S8‑Ni3S2 / NCF to prepare partially nickel-doped cobalt spinel (Ni x Co 3‑x O4‑Ov‑SO4 2‑ ), which can enhance the leaching of SO4 from the initial phase compared to cobalt spinel 2‑ The adsorption capacity was improved to achieve an overall water splitting time of more than 600 h at a current density of 1000 mA cm ‑2 , and has excellent activity. Co9S8‑Ni3S2 / NCF is transformed into SO4 2‑ Adsorbed nickel-doped SO4 2‑ Cobalt spinel, at 1000mA cm ‑2 Under these conditions, the oxygen evolution reaction (OER) stability of 1000 hours was achieved. In situ Raman spectroscopy and XPS results show that the partial substitution of nickel atoms for cobalt atoms enhances the SO4 2‑ The adsorption capacity is improved, thereby promoting the formation of high-density active sites and accelerating the interfacial electron transfer at high current density.

Description

Technical Field

[0001] The present invention relates to the field of catalyst technology, in particular to a method for self-reconstruction of Co9S8-Ni3S2 / NCF into Ni x Co 3- x O4-Ov-SO4 2- / NCF method to enhance the activity and stability of oxygen evolution reaction. Background Art

[0002] The search has long been on for ways to produce electricity that is both cheap and clean. Hydrogen is considered an ideal energy storage medium due to its extremely high energy storage density and clean combustion products. Large-scale production of hydrogen by water electrolysis using renewable energy has been identified as a promising solution to the energy challenge. Extensive research has shown that the key to improving the energy conversion efficiency of this process lies in reducing the overpotentials associated with the cathode hydrogen evolution reaction (HER) and the anode oxygen evolution reaction (OER). Theoretically, the minimum energy input required for HER and OER is ΔG = 237.1 kJ mol -1 , the corresponding potential is 1.23 V. However, the total overpotential is affected by factors such as gas phase release and interfacial charge transfer resistance, and can be expressed as: η total =η act +η Ohm +η con , where η act is the overpotential required to activate the reaction [3] . Researchers have invested a lot of effort to reduce this value. It is generally believed that noble metal catalysts exhibit the highest activity and the lowest Tafel slope. However, their high cost has prompted the search for alternatives suitable for large-scale applications. In addition, reaction conditions, especially the acidity of the electrolyte, significantly affect the performance of the catalyst. Alkaline water splitting has become a strong candidate for commercial applications, which emphasizes the need for catalysts compatible with these conditions. Therefore, highly active and durable non-noble metal electrocatalysts are urgently needed to achieve industrial-scale water splitting and pave the way for the development of energy systems.

[0003] As a potential water splitting catalyst, TMS exhibits semiconductor-like conductivity and fast charge transfer kinetics due to its relatively narrow band gap and the asymmetry of certain coordinated unsaturated surface cations. Compared with TMS as a cathode, its stability as an anode is poor. This is because during the OER process, TMS usually undergoes in situ conversion or reconstruction into oxides / oxyhydroxides in alkaline media, and in the process, it leaches water-soluble SO4 2-. In addition, the increase in lattice defects during the reconstruction process can improve activity, but this can also lead to structural instability, resulting in a trade-off between activity and stability. Although the reconstruction process is often regarded as a challenge for long-term stability, it also provides an opportunity to improve catalytic performance by interacting with surface-adsorbed oxygen anions and newly formed oxides. Surface-adsorbed oxygen anions can significantly reduce the reaction energy barrier and enhance the oxygen evolution reaction (OER) activity by optimizing the adsorption energy of various intermediates. Although significant breakthroughs have been made in recent years in optimizing the binding energy and overpotential of intermediates through surface-adsorbed oxygen anions, they can serve as anodes in alkaline media at high current densities (such as 1000 mA cm -2 or higher) for a long time are still very limited. Summary of the Invention

[0004] The purpose of the present invention is to provide a Co9S8-Ni3S2 / NCF self-reconstructed into Ni x Co 3-x O4-Ov-SO4 2- / NCF enhances the activity and stability of oxygen evolution reaction to solve the above problems.

[0005] To achieve the above object, the present invention provides a Co9S8-Ni3S2 / NCF self-reconstructed into Ni x Co 3-x O4-Ov-SO4 2- The method of enhancing the activity and stability of the oxygen evolution reaction by using NCF includes the following steps:

[0006] Step 1: First, synthesize Co9S8-Ni3S2 / NCF needle-leaf nanochains by reacting NCF with 78 mg of sulfur powder at 160 °C for 6 hours;

[0007] Step 2: HER and OER performance analysis of Co9S8-Ni3S2 / NCF;

[0008] In step 3, Co9S8-Ni3S2 / NCF was used as the anode and cathode of a 1 M KOH electrolytic cell. Compared with the cathode, the rod-like particles formed on the anode side indicated the complete reconstruction of the catalyst, and Ni x Co 3-x O4-Ov-SO4 2- / NCF; Co9S8-Ni3S2 / NCF transforms into Ni during high current density water electrolysis x Co 3-x O4-Ov-SO4 2- , obtaining high-performance and high-stability OER electrocatalysts;

[0009] Step 4: Ni xCo 3-x O4-Ov-SO4 2- / NCF was analyzed by XPS to explore the Co9S8-Ni3S2 / NCF at 1000mAcm -2 Surface chemical state after 1070 hours of OER test;

[0010] Step 5: Perform XPS analysis on Co9S8-Ni3S2 / NCF after 20 hours of anodic reaction, and compare the results with those in step 4.

[0011] Step 6: Further study the self-reconstruction process using in situ Raman spectroscopy and conclude that Ni is partially substituted in Co3O4 to form Ni x Co 3-x SO4 leached during O4 enhanced reconstruction 2- Adsorption on the surface of the new phase increases the strength and quantity of adsorption; more SO4 2- Adsorption on the catalyst surface is conducive to the generation of more active sites; SO4 2- The higher adsorption strength of SO4 is conducive to the long-term stability of these active sites under high current density catalytic conditions; 2- Adsorption at oxygen vacancies can stabilize surface defect sites, which is beneficial for long-term catalytic stability.

[0012] Preferably, in the above-mentioned Co9S8-Ni3S2 / NCF self-reconstruction to Ni x Co 3-x O4-Ov-SO4 2- In the method for enhancing the activity and stability of oxygen evolution reaction using NCF, the mass ratio of cobalt to nickel in the NCF in step 1 is 5.72:1.

[0013] Preferably, in the above-mentioned Co9S8-Ni3S2 / NCF self-reconstruction to Ni x Co 3-x O4-Ov-SO4 2- In the method for enhancing the activity and stability of oxygen evolution reaction (HER) by using Co9S8-Ni3S2 / NCF, the specific analysis process of the HER performance in step 2 is as follows: the electrochemical performance of HER is evaluated by a three-electrode system in a 1M KOH solution; the linear sweep voltammetry is used at 1mV s -1 Typical polarization curves were obtained at a scan rate of 10 mA cm and 90% iR compensation was applied; -2 The overpotential of Co9S8-Ni3S2 / NCF sample was measured to be 59mV at 1000mA cm -2When the overpotential of Co9S8-Ni3S2 / NCF was recorded as 328 mV, the Tafel slope of Co9S8-Ni3S2 / NCF was calculated to be 49.4 mV dec -1 The measured charge transfer resistance values ​​of Co9S8-Ni3S2 / NCF are 28.2Ω, 12.36Ω, 3.15Ω and 0.77Ω, respectively.

[0014] Preferably, in the above-mentioned Co9S8-Ni3S2 / NCF self-reconstruction to Ni x Co 3-x O4-Ov-SO4 2- In the method for enhancing the activity and stability of oxygen evolution reaction (OER) of Co9S8-Ni3S2 / NCF, the specific analysis process of the OER performance in step 2 is as follows: the electrochemical performance of OER is evaluated by a three-electrode system in 1M KOH solution; the polarization curve is obtained by linear sweep voltammetry; the sample continuously exhibits an oxidation peak at low current density, and the Tafel slope of Co9S8-Ni3S2 / NCF is 65.4mV dec-1, R ct The value is 1.14Ω, Co9S8-Ni3S2 / NCF at 1000mA cm -2 The OER activity of Co9S8-Ni3S2 / NCF was tested under the conditions of 10 mA cm-1, and the activity increased slightly in the initial stage. The reverse scanning LSV curve showed that the OER activity reached the optimal level after 1.5 h of constant potential test. -2 and 1000mA cm -2 The overpotentials at these temperatures are 174 mV and 423 mV, respectively.

[0015] Preferably, in the above-mentioned Co9S8-Ni3S2 / NCF self-reconstruction to Ni x Co 3-x O4-Ov-SO4 2- In the method for enhancing the activity and stability of oxygen evolution reaction by using / NCF, the Co9S8-Ni3S2 / NCF in step 3 is heated to 1000 mA cm -2 Under long-term operation, it is reconstructed into Ni x Co 3-x O4-Ov-SO4 2- / NCF.

[0016] Preferably, in the above-mentioned Co9S8-Ni3S2 / NCF self-reconstruction to Ni x Co 3-x O4-Ov-SO4 2- In the method for enhancing the activity and stability of oxygen evolution reaction by using NCF, the Nix Co 3-x O4-Ov-SO4 2- The corresponding mapping images and EDS of / NCF show that the Co, Ni, S and O elements are evenly distributed on the surface of the reconstructed species, while the O content increases significantly and the S content decreases.

[0017] Preferably, in the above-mentioned Co9S8-Ni3S2 / NCF self-reconstruction to Ni x Co 3-x O4-Ov-SO4 2- In the method for enhancing the activity and stability of oxygen evolution reaction by using NCF, the Ni x Co 3-x O4-Ov-SO4 2- XPS analysis of Co9S8-Ni3S2 / NCF showed that the -2 After 1070 hours of OER test, Ni 3+ Replaces some of the Co in the octahedral vacancies 3+ , forming a normal spinel structure, and a large amount of sulfur elements are leached during the phase change process, and these elements are oxidized to SO4 2- and adsorbed on Ni x Co 3-x O4-Ov surface.

[0018] Preferably, in the above-mentioned Co9S8-Ni3S2 / NCF self-reconstruction to Ni x Co 3-x O4-Ov-SO4 2- In the method of enhancing the activity and stability of oxygen evolution reaction by using NCF, the comparison of the analytical results in step 4 and step 5 shows that cobalt spinel has been formed in the early stage of the test, and Co 2p 3 / 2 The narrow peak splits into Co 2+ and Co 3+ The broad peak and sharp peak of Ni 2p at 855.7eV 3 / 2 The peak corresponds to Ni 3+ ; These results confirm that the reconstructed Ni x Co 3-x O4-Ov-SO4 2- No secondary transformations were experienced during the long-term high current density OER process.

[0019] Preferably, in the above-mentioned Co9S8-Ni3S2 / NCF self-reconstruction to Ni x Co 3-x O4-Ov-SO4 2-In the method of enhancing the activity and stability of oxygen evolution reaction by using NCF, the research process in step 6 is as follows: in the initial state, the peak associated with Ni3S2 is observed, and the peak attributed to Co9S8 is also observed. As the applied potential gradually increases, the peak intensity of the Ni-O and SO bands of Co9S8-Ni3S2 increases, while the intensity associated with the Ni-S and Co-S bands decreases at the same time. The SO peak intensity of Co9S8 is particularly weak, indicating that Co9S8-Ni3S2 has a strong effect on SO4 2- The adsorption capacity is stronger, which is related to the presence of Ni. It is known that Ni incorporation has an effect on the reconstructed surface SO4 2- The promotion effect of adsorption.

[0020] Therefore, the present invention adopts a Co9S8-Ni3S2 / NCF structure to self-reconstruct Ni x Co 3-x O4-Ov-SO4 2- / NCF enhances the activity and stability of oxygen evolution reaction, and adopts the self-reconstruction strategy of Co9S8-Ni3S2 / NCF to prepare partially nickel-doped cobalt spinel (Ni x Co 3-x O4-Ov-SO4 2- ), which can enhance the leaching of SO4 from the initial phase compared to cobalt spinel 2- The adsorption capacity was improved to achieve an overall water splitting time of more than 600 h at a current density of 1000 mA cm -2 , and has excellent activity. Co9S8-Ni3S2 / NCF is transformed into SO4 2- Adsorbed nickel-doped SO4 2- Cobalt spinel, at 1000mA cm -2 Under these conditions, the oxygen evolution reaction (OER) stability of 1000 hours was achieved. In situ Raman spectroscopy and XPS results showed that the partial substitution of nickel atoms for cobalt atoms enhanced the SO4 2- The adsorption capacity promotes the formation of high-density active sites and accelerates the interfacial electron transfer at high current density. Density functional theory (DFT) calculations show that the leached SO4 2- The adsorption stabilizes the surface oxygen vacancies and optimizes the adsorption energy of the intermediates, thereby improving the stability and catalytic performance.

[0021] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Preparation of Co9S8-Ni3S2 / NCF and Ni on NCF substrate in the embodiment of the present invention x Co3-x O4-Ov-SO4 2- / Flow chart of the preparation of NCF substrate;

[0023] Figure 2 Electrochemical performance of Co9S8-Ni3S2 / NCF and control samples in 1.0 M KOH medium, including (a) HER polarization curve, (b) Tafel slope, (c) Nyquist plot, (d) OER polarization curve, (e) Tafel slope, (f) Nyquist plot, (g) Co9S8-Ni3S2 / NCF at 1000 mA cm -2 The OER test process was carried out under the conditions of (h) Co9S8-Ni3S2 / NCF at 1000mA cm -2 Performance of the OER process for 0.5-2 h at 400 nm, (i) Polarization curves of Co9S8-Ni3S2 / NCF after 1.5 h of OER and immersion in fresh electrolyte for 3 h, (j) Polarization curves of Co9S8-Ni3S2 / NCF at current densities of 10, 100, 200, and 500 mA cm -2 The overpotential of Co9S8-Ni3S2 / NCF after 1.5 h of OER process is compared with that of RuO2 / NCF, and other state-of-the-art HER (k) and OER (l) electrocatalysts at 10 mA cm -2 Compare the overpotential at and the corresponding Tafel slope;

[0024] Figure 3 Electrochemical performance of Co9S8-Ni3S2 / NCF according to the present invention and the control sample in 1.0 M potassium hydroxide. MA (a) and TOF (b) represent HER. MA (c) and TOF (d) represent OER.

[0025] Figure 4 CV curves (left) of the electrode prepared at different scan rates from 20 to 200 mV in 1 M potassium hydroxide according to the embodiment of the present invention and the calculated C dl (right). (a, b) Co9S8-Ni3S2 / NCF, (c, d) NiS x / NF and (e, f)Co9S8 / CF;

[0026] Figure 5 This is a digital photograph of the contact angle of bubbles on the catalyst of an embodiment of the present invention;

[0027] Figure 6 The present invention is a method for self-reconstructing Co9S8-Ni3S2 / NCF into Ni x Co 3-x O4-Ov-SO4 2-Durability and overall water splitting performance of Co9S8-Ni3S2 / NCF in the embodiment of the method for simultaneously enhancing the oxygen evolution reaction activity and stability of / NCF, with water added again at the sawtooth point; (a) Co9S8-Ni3S2 / NCF in 1 M KOH at 1000 mA cm -2 Oxygen evolution reaction (OER) stability fingerprint of the proposed method; (b) comparison with other reported OER stability; (c) at 1000 mA cm -2 The stability of hydrogen evolution reaction (HER) was tested at a current density of 1000 mA cm-1. (d) and (e) are the LSV curves and corresponding Nyquist plots of Co9S8-Ni3S2 / NCF||Co9S8-Ni3S2 / NCF-based electrolyzer and Pt / C / NCF||RuO2 / NCF-based electrolyzer, respectively. (f) The stability of hydrogen evolution reaction (HER) was tested at a current density of 1000 mA cm-1. (g) The LSV curves and corresponding Nyquist plots of Co9S8-Ni3S2 / NCF||Co9S8-Ni3S2 / NCF-based electrolyzer and Pt / C / NCF||RuO2-based electrolyzer were respectively. -2 Stability test under 1000 mA cm -2 The overall water splitting stability was compared under different current densities;

[0028] Figure 7 The Co9S8-Ni3S2 / NCF||Co9S8-Ni3S2 / NCF-based electrolytic cell of the embodiment of the present invention is subjected to a current density of 1000 mA cm -2 Compare the voltage under with others;

[0029] Figure 8 The HER of the embodiment of the present invention is -200mA cm -2 (a) and OER at 150 mA cm -2 (b) durability test;

[0030] Figure 9 (a) Co9S8-Ni3S2 / NCF sample of the present invention contains j 1000 Morphology of the HER process in 1 M potassium hydroxide solution; (b) corresponding SEM-EDS spectrum;

[0031] Figure 10 This is the SEM-EDS spectrum analysis of the Co9S8-Ni3S2 / NCF needle-leaf nanochains according to the embodiment of the present invention;

[0032] Figure 11 The embodiment of the present invention is at 1000mA cm -2XPS spectrum of Co9S8-Ni3S2 / NCF after 150h stability measurement under the same conditions;

[0033] Figure 12 The embodiment of the present invention is at 100mA cm -2 XPS spectrum of Co9S8-Ni3S2 / NCF after 50h stability measurement under the same conditions;

[0034] Figure 13 The embodiment of the present invention is at 1000mA cm -2 XPS spectrum of Co9S8-Ni3S2 / NCF after 150h stability measurement under the same conditions;

[0035] Figure 14 The new phase Ni is converted from Co9S8-Ni3S2 / NCF in the OER process of the embodiment of the present invention. x Co 3- x Characterization of O4-Ov-; (a) Ni x Co 3-x SEM images of O4-Ov-; (b, c)Ni x Co 3-x TEM image of O4-Ov- (the inset is SAED pattern) and high-resolution TEM image; (d) Ni x Co 3-x HAADF-STEM images and corresponding elemental mapping of O4-Ov-; Co 2p (e), Ni 2p (f), S2p (g), O 1s (h) of Co9S8-Ni3S2 / NCF (before OER) and Ni x Co 3-x XPS spectra of O4-Ov- (after OER); (i) in situ Raman spectra of Co9S8-Ni3S2 / NCF (top) and Co9S8 / NCF (bottom) at different potentials;

[0036] Figure 15 SEM mapping images of the Co9S8-Ni3S2 / NCF sample in a 1 M potassium hydroxide solution at j1000 for 50 h in Example (ae) of the present invention; (f) corresponding SEM-EDS spectrum;

[0037] Figure 16 The embodiment of the present invention is at 1000mA cm -2 HRTEM image of Co9S8-Ni3S2 / NCF after 1070h stability measurement under OER conditions;

[0038] Figure 17200 mA cm in HER (a) and OER (b) of the embodiment of the present invention. -2 XRD pattern of Co9S8-Ni3S2 / NCF after stability measurement under ;

[0039] Figure 18 (a) The morphology of the Co9S8-Ni3S2 / NCF sample in 1000 and 1000 solutions for 1070 h; (b) the corresponding SEM-EDS spectrum of the embodiment of the present invention;

[0040] Figure 19 The Co9S8-Ni3S2 / NCF and Co9S8 / CF of the present invention are shown in Figure 1 at 1000 mA cm -2 XPS spectra after stable measurement for 20 h under OER conditions;

[0041] Figure 20 The Co9S8-Ni3S2 / NCF of the embodiment of the present invention is 1000mA cm -2 Polarization curves after 100h it test under . DETAILED DESCRIPTION

[0042] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] Referring to the accompanying drawings, the present application provides a method for self-reconstruction of Co9S8-Ni3S2 / NCF into Ni x Co 3-x O4-Ov-SO4 2- The method of enhancing the activity and stability of the oxygen evolution reaction by using NCF includes the following steps:

[0044] Step 1: First, synthesize Co9S8-Ni3S2 / NCF needle-leaf nanochains by reacting NCF with 78 mg of sulfur powder at 160 °C for 6 hours;

[0045] Step 2: HER and OER performance analysis of Co9S8-Ni3S2 / NCF;

[0046] In step 3, Co9S8-Ni3S2 / NCF was used as the anode and cathode of a 1 M KOH electrolytic cell. Compared with the cathode, the rod-like particles formed on the anode side indicated the complete reconstruction of the catalyst, and Ni x Co 3-x O4-Ov-SO42- / NCF; Co9S8-Ni3S2 / NCF transforms into Ni during high current density water electrolysis x Co 3-x O4-Ov-SO4 2- , obtaining high-performance and high-stability OER electrocatalysts;

[0047] Step 4: Ni x Co 3-x O4-Ov-SO4 2- / NCF was analyzed by XPS to explore the Co9S8-Ni3S2 / NCF at 1000mAcm -2 Surface chemical state after 1070 hours of OER test;

[0048] Step 5: Perform XPS analysis on Co9S8-Ni3S2 / NCF after 20 hours of anodic reaction, and compare the results with those in step 4.

[0049] Step 6: Further study the self-reconstruction process using in situ Raman spectroscopy and conclude that Ni is partially substituted in Co3O4 to form Ni x Co 3-x SO4 leached during O4 enhanced reconstruction 2- Adsorption on the surface of the new phase increases the strength and quantity of adsorption; more SO4 2- Adsorption on the catalyst surface is conducive to the generation of more active sites; SO4 2- The higher adsorption strength of SO4 is conducive to the long-term stability of these active sites under high current density catalytic conditions; 2- Adsorption at oxygen vacancies can stabilize surface defect sites, which is beneficial for long-term catalytic stability.

[0050] The mass ratio of cobalt to nickel in NCF in step 1 is 5.72:1.

[0051] To further optimize the above technical solution, the specific analysis process of the HER performance in step 2 is as follows: the electrochemical performance of Co9S8-Ni3S2 / NCF was evaluated using a three-electrode system in 1M KOH solution; linear sweep voltammetry was used at 1mV s -1 Typical polarization curves were obtained at a scan rate of 10 mA cm and 90% iR compensation was applied; -2 The overpotential of Co9S8-Ni3S2 / NCF sample was measured to be 59mV at 1000mA cm -2 When the overpotential of Co9S8-Ni3S2 / NCF was recorded as 328 mV, the Tafel slope of Co9S8-Ni3S2 / NCF was calculated to be 49.4 mV dec-1 The measured charge transfer resistance values ​​of Co9S8-Ni3S2 / NCF are 28.2Ω, 12.36Ω, 3.15Ω and 0.77Ω, respectively.

[0052] The specific analysis process of the OER performance in step 2 is as follows: the electrochemical performance of Co9S8-Ni3S2 / NCF in 1MKOH solution is evaluated using a three-electrode system; the polarization curve is obtained by linear sweep voltammetry; the sample continuously shows an oxidation peak at low current density, and the Tafel slope of Co9S8-Ni3S2 / NCF is 65.4mV dec -1 , R ct The value is 1.14Ω, Co9S8-Ni3S2 / NCF at 1000mA cm -2 The OER activity of Co9S8-Ni3S2 / NCF was tested under the conditions of 10 mA cm-1, and the activity increased slightly in the initial stage. The reverse scanning LSV curve showed that the OER activity reached the optimal level after 1.5 h of constant potential test. -2 and 1000mA cm -2 The overpotentials at these temperatures are 174 mV and 423 mV, respectively.

[0053] Specifically, the performance analysis and comparative analysis of Co9S8-Ni3S2 / NCF in HER and OER in step 2 are as follows:

[0054] Co9S8-Ni3S2 / NCF and control samples NCF, NiS x The electrochemical performance of HER on Pt / NF and Pt / C was evaluated using a three-electrode system in 1 M KOH solution. Linear sweep voltammetry (LSV) was used at a speed of 1 mV s -1 A typical polarization curve was obtained at a scan rate of 100 nm and 90% iR compensation was applied, as shown in Figure 2 (a). At 10 mA cm -2 (j 10 ) when NCF, NiS x The overpotentials of Co9S8-Ni3S2 / NCF, Co9S8-Ni3S2 / NF and Pt / C samples were measured to be 211 mV, 99 mV, 59 mV and 30 mV, respectively. The catalytic activity of Co9S8-Ni3S2 / NCF heterostructure was significantly better than that of Co9S8 / CF and NiS x / NF. As for 1000mA cm -2 (j 1000 ), the overpotential record is 528mV for NCF and 528mV for NiS x / NF is 387mV, Co9S8 / CF is 473mV, and Co9S8-Ni3S2 / NCF is 328mV. 1000 The data at this time cannot be determined. In addition, the Tafel slope of Co9S8-Ni3S2 / NCF was calculated to be 49.4mV dec -1 , which is much better than other control samples, such as Figure 2 (b) This indicates that the hydrogen evolution of Co9S8-Ni3S2 / NCF catalysis is mainly carried out through the Volmer-Heyrovsky pathway. x The charge transfer resistance (R ct ) values ​​are 28.2Ω, 12.36Ω, 3.15Ω and 0.77Ω respectively. Figure 2 (c) shows that this reflects the faster interfacial dynamics in the heterostructure. Mass activity (MA), which represents the current yield per unit mass, is a key indicator for evaluating catalyst performance. Figure 3 Turnover frequency (TOF) is an objective criterion used to quantify the reaction rate of each active catalytic site under specific conditions, which reveals the specific activity of these sites, such as Figure 3 (b) clearly shows that the activity of Co9S8-Ni3S2 / NCF is significantly improved compared with its control sample.

[0055] Compared with the relatively simple HER, OER presents a more complex situation, mainly due to the slow kinetics of its four electron transfer steps. The experimental conditions of OER are similar to those of HER. The polarization curves of five different catalyst samples were obtained by linear sweep voltammetry (LSV). Figure 2 (d) The sample continues to show an oxidation peak at low current density, indicating that some changes are taking place. The Tafel slope of Co9S8-Ni3S2 / NCF is 65.4mVdec -1 , which is significantly higher than NCF, Co9S8 / CF and NiS x / NF, indicating that its kinetic characteristics are close to the values ​​of RuO2, such as Figure 2 (e) In addition, R ct The values ​​are 25.1Ω, 2.69Ω, 10.71Ω and 1.14Ω, corresponding to NCF, Co9S8 / CF, NiS x / NF and Co9S8-Ni3S2 / NCF, such as Figure 2 (f) shows that Co9S8-Ni3S2 / NCF exhibits the lowest R ctThe MA and TOF values ​​shown in Figures S11(c) and S11(d) indicate that its performance is comparable to that of commercial RuO2. Figure 2 (g) shows the Co9S8-Ni3S2 / NCF and Co9S8 / CF at 1000 mA cm -2 Despite the obvious difference in stability between the two, Co9S8-Ni3S2 / NCF showed a slight increase in activity in the initial stage, indicating the benefit of self-reconstruction. Figure 2 (h) Further confirms the changes in OER activity observed in the stability test. To eliminate potential interference, the reverse scan LSV curve was analyzed. After 1.5 h of constant potential testing, the OER activity reached the optimal level at 10 mA cm -2 and 1000mA cm -2 However, after immersing the Co9S8-Ni3S2 / NCF in fresh 1M KOH for 3 h after 1.5 h of constant potential test, the OER activity decreased significantly, indicating that certain adsorbed species may have an important influence on the activity during the reconstruction process, such as Figure 2 (i) In addition, Figure 2 (j) shows that the overpotential of the self-reconstructed phase is still lower than that of RuO2 at different current densities. Finally, the HER performance of the sulfide heterostructure and the OER performance of the newly formed species show advanced characteristics compared with the excellent values ​​in recent studies, highlighting their important research value, such as Figure 2 (k) and Figure 2 (l) shown. Figure 4 (a), (c) and (e) depict the Co9S8-Ni3S2 / NCF, NiS x Cyclic voltammetry (CV) of Co9S8 / CF and Co9S8 / NF at different scan rates. Figure 4 (b), (d), and (f) present the double layer capacitance (C dl ) fitting curve. Given the relationship between electrochemically active surface area (ECSA) and C dl Co9S8-Ni3S2 / NCF shows the highest C dl , measured to be 22.0mF cm -2 This is attributed to the unique structure formed by the sulfurization of bimetallic foam, which enables it to obtain the largest ECSA and promotes more complete contact between the heterostructure and the electrolyte. Figure 5As shown, the high bubble contact angle of 142° and the low sliding onset angle of 1.9° demonstrate the superoleophobicity of the Co9S8-Ni3S2 / NCF surface. Furthermore, the low adhesion of the bubbles to the catalyst surface helps to improve the gas-phase desorption kinetics, thereby minimizing the potential detrimental effects of bubble collisions on the catalyst structural stability.

[0056] To further optimize the above technical solution, in step 3, Co9S8-Ni3S2 / NCF was -2 Under long-term operation, it is reconstructed into Ni x Co 3-x O4-Ov-SO4 2- / NCF.

[0057] Step 3 Ni x Co 3-x O4-Ov-SO4 2- The corresponding mapping images and EDS of / NCF show that the Co, Ni, S and O elements are evenly distributed on the surface of the reconstructed species, while the O content increases significantly and the S content decreases.

[0058] It should be noted that the specific analysis process of the practical application potential of Co9S8-Ni3S2 / NCF and the control group as the anode and cathode of the 1M KOH electrolytic cell in step 3 in the overall water splitting is as follows:

[0059] The electrolytic cell based on Co9S8-Ni3S2 / NCF showed significantly superior performance compared to the electrolytic cell based on Pt / C / NCF||RuO2 / NCF, such as Figure 6 (d) When the battery voltage exceeds 1.71 V, the advantages of Co9S8-Ni3S2 / NCF become obvious, respectively at a geometric current density of 500 mA cm -2 and 1000mA cm -2 Only 1.90V and 1.99V were required for the electrolysis. After 100 hours of operation, the cell voltage dropped to 1.89V and 1.97V, indicating that new active sites may have formed on our Co9S8-Ni3S2 / NCF sample. These values ​​are not only lower than the 2.02V and 2.15V required for the Pt / C / NCF||RuO2 / NCF-based electrolyzer, but also better than many recently developed advanced non-precious metal catalysts such as Figure 7 shown. Figure 6The Nyquist plot in (e) further shows that the electrolyzer based on Co9S8-Ni3S2 / NCF exhibits lower interfacial contact resistance and solution resistance than the electrolyzer based on Pt / C / NCF||RuO2 / NCF, indicating its superior interfacial electron transfer ability and intrinsic conductivity. It is worth noting that after 100 hours of overall water splitting test, the interfacial electron transfer ability of the catalyst was enhanced, which is consistent with the Figure 8 (b) and Figure 6 The long-term stability of the overall water splitting catalyst is crucial for the industrial application of the catalyst. Figure 6 (f) shows that the electrolyzer based on Co9S8-Ni3S2 / NCF can stably split water with minimal performance degradation over a time span of more than 600 hours, while the electrolyzer based on Pt / C / NCF||RuO2 / NCF shows rapid performance degradation. This performance significantly exceeds the recent 1000mA cm -2 Other advanced catalysts tested at current density Figure 6 (g), marking it as a highly promising material for large-scale electrolytic hydrogen production.

[0060] In order to further optimize the above technical solution, in step 4, Ni x Co 3-x O4-Ov-SO4 2- XPS analysis of Co9S8-Ni3S2 / NCF showed that the -2 After 1070 hours of OER test, Ni 3+ Replaces some of the Co in the octahedral vacancies 3+ , forming a normal spinel structure, and a large amount of sulfur elements are leached during the phase change process, and these elements are oxidized to SO4 2- and adsorbed on Ni x Co 3-x O4-Ov surface.

[0061] Comparison of the analytical results in Step 4 and Step 5 shows that cobalt spinel has formed in the early stages of the test and Co 2p 3 / 2 The narrow peak splits into Co 2+ and Co 3+ The broad peak and sharp peak of Ni 2p at 855.7eV 3 / 2 The peak corresponds to Ni 3+ ; These results confirm that the reconstructed Ni x Co 3-x O4-Ov-SO4 2- No secondary transformations were experienced during the long-term high current density OER process.

[0062] Specifically, the analysis and comparison process of steps four and five is as follows:

[0063] Generally, the continuous attack of hydroxide ions on metal sulfides will lead to the partial replacement of surface -S groups by -OH or -O functional groups during the HER process, which is generally regarded as an activation process of non-noble metal sulfides and phosphides, which may enhance their catalytic activity in HER. -2 After 100 hours of HER, the morphology of the needle-like nanochains changed slightly. Figure 9 (a) SEM-EDS shows that the surface -S groups are partially replaced by -OH or -O groups Figure 9 (b) The sulfur content on the catalyst surface decreased from 38.55 to 16.27 atomic% after HER. Figure 10 As shown in Figure 2, the oxygen content increased from 1.72 to 40.55 atomic%. XPS analysis revealed that at 1000 mA cm -2 Next, Co 3+ and Ni 2+ Almost completely lost, such as Figure 11 As shown, this is consistent with the 100mA cm -2 The observed decrease is consistent with the Figure 12 This observation suggests that the HER process affects the catalyst similarly at high and low current densities, characterized by preferential dissociation of low binding energy components. Typically, low binding energy components are less strongly bound to other atoms, which may make them more susceptible to degradation. However, this suggests that the heterointerface remains intact and continues to serve as an active site under high HER current density conditions, such as Figure 13 As shown. Further through the CV curve and C dl The changes of ECSA before and after HER were studied, as shown in Figures S22a and S22b. dl The value is 21.4mF cm -2 , compared to the initial value of 22.0mF cm -2 This indicates minimal corrosion, demonstrating that the Co9S8-Ni3S2 heterostructure maintains its fundamental stability during hydrogen evolution at high current density.

[0064] The rod-like particles formed on the anode side compared to the cathode side indicate the complete reconstruction of the catalyst as Figure 14 The corresponding mapping diagram and EDS show that the Co, Ni, S and O elements are evenly distributed on the surface of the reconstructed species, while the O content increases significantly and the S content decreases, as shown in Figure 2. Figure 15 As shown. By TEM, the new phase was preliminarily identified as partially covered by Ni 3+The substituted spinel Co3O4 was further confirmed by XPS and in situ Raman analysis, and the presence of surface-anchored sulfate groups was verified, which led to the name Ni x Co 3-x O4-Ov-SO4 2- The SAED pattern shows that the radius of the diffraction ring corresponds to a specific crystal plane of Co3O4, proving that it has polycrystalline characteristics, such as Figure 14 (b). Figure 14 The interplanar spacing shown in (c) is measured to be 0.203 nm, which is slightly larger than the 0.202 nm required for spinel Co3O4(400), which is due to the incorporation of Ni atoms. High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images and corresponding EDS mapping images show that Co, Ni, O, and S are uniformly distributed within the product, as shown in Figure 2. Figure 14 (d). Figure 16 , further confirming the small grain size and extensive amorphous regions of the new phase, which helps to explain the Figure 17 It is noteworthy that the exposed crystal planes of these grains correspond to Co3O4(400), as shown in Figure 16 , which suggests that the reconstruction during the electrocatalytic reaction may be related to crystal face engineering. XPS analysis was further performed to explore the Co9S8-Ni3S2 / NCF at 1000mA cm -2 The surface chemical state after 1070 hours of OER test. Figure 14 As shown in (e), the Co 2p emission spectrum is best fitted to two spin-orbit doublets, namely Co 3+ (779.7 eV) and Co 2+ (781.0eV), and an oscillatory satellite peak (labeled as "Sat."). Figure 14 As shown in (f), the Ni 2p spectrum corresponds only to Ni x Co 3-x Ni in O4 3+ The spin-orbit doublet characteristics, specifically 2p 3 / 2 (855.6 eV) and 2p 1 / 2 (873.1eV) orbital, and related satellite peaks. This indicates that Ni 3+ Replaces some of the Co in the octahedral vacancies 3+ , forming a normal spinel structure. Figure 14 As shown in (g), compared with the initial sample, the O1s spectrum shows a clear characteristic peak (529.1eV) associated with the spin-orbit peak of the metal-O bond. The dominance of the oxygen vacancy peak indicates the abundance of surface defect sites, which is believed to introduce additional conductive carriers and may enhance the conductivity and catalytic performance of the material.

[33] However, as the defect concentration increases, the periodicity of the crystal structure may decrease because the disorder of the atomic arrangement increases the energy of the system, which is detrimental to stability. Figure 14 As shown in (h), the S2p spectrum reveals that a large amount of sulfur is leached during the phase transition, and these elements are oxidized to SO4 2- (168.3eV) and adsorbed on Ni x Co 3-x O4-Ov surface. After 1070 hours of OER test, the surface of the catalyst becomes rougher, such as Figure 18 (a); However, the element ratios of Co, Ni, S and O are still the same as those of Ni x Co 3-x O4-Ov are consistent, such as Figure 18 (b). In addition, a small amount of S can still be detected on the surface. Comparison of these findings with the XPS results after 20 hours of anodic reaction indicates that cobalt spinel has formed in the early stages of the test, and Co 2p 3 / 2 The narrow peak splits into Co 2+ and Co 3+ The broad peaks and sharp peaks are as follows Figure 19 (a). Meanwhile, the Ni 2p at 855.7eV 3 / 2 The peak corresponds to Ni 3+ ,like Figure 19 (b). These results confirm that the reconstructed Ni x Co 3-x O4-Ov-SO4 2- It does not undergo any secondary transformation during the long-term high current density OER process, demonstrating its stability as a new catalyst.

[0065] To further optimize the above technical solution, the research process in step six is ​​as follows: In the initial state, the peak associated with Ni3S2 is observed, and the peak attributed to Co9S8 is also observed. As the applied potential gradually increases, the peak intensity of the Ni-O and SO bands of Co9S8-Ni3S2 increases, while the intensity associated with the Ni-S and Co-S bands decreases at the same time. The SO peak intensity of Co9S8 is particularly weak, indicating that Co9S8-Ni3S2 has a strong effect on SO4 2- The adsorption capacity is stronger, which is related to the presence of Ni. It is known that Ni incorporation has an effect on the reconstructed surface SO4 2- The promotion effect of adsorption.

[0066] Specifically, the analysis process of step six is ​​as follows:

[0067] The reconstruction dynamics of Co9S8-Ni3S2 and Co9S8 were further studied using in situ Raman spectroscopy. Figure 14(i), all voltages are relative to the reversible hydrogen electrode. In the initial state, peaks related to Ni3S2 were observed at 302 cm -1 and 323cm -1 , and peaks attributed to Co9S8 were also observed at 240 cm -1 、465cm -1 and 671cm -1 , and the presence of surface oxide species. As the applied potential gradually increases, the peak intensities of the Ni-O and SO bands of Co9S8-Ni3S2 increase, while the intensities associated with the Ni-S and Co-S bands decrease simultaneously. The SO peak intensity of Co9S8 is particularly weak, indicating that Co9S8-Ni3S2 undergoes SO4 2- The adsorption capacity of Co3O4 is stronger, which is related to the presence of Ni. -1 (E g ) peak can be identified in the initial state, confirming the relatively low oxygen content on the Co9S8-Ni3S2 surface, as shown in 10. It is worth noting that at high overpotential, the 465cm -1 The peak disappears completely and is replaced by the E g The peak substitution indicates the breaking of Co-S bonds and the in-situ formation of Co-O bonds inside the Co9S8 crystal. -1 A broad peak appears near the surface, which becomes sharper with increasing voltage, which is attributed to the F 2g peak at 677 cm, which indicates that the crystalline characteristics of the reconstructed phase are enhanced with increasing overpotential. -1 The peak is related to the Co-S bond and shows an obvious red shift and intensity decrease with increasing voltage, reflecting the weakening of Co-S bond vibration and the decrease in intensity. Figure 19 The S2p peak of Co9S8 / CF in (c) is almost negligible, further confirming the effect of Ni incorporation on the reconstructed surface SO4 2- In addition, Figure 19 The abnormally high Co observed in (a) 2+ level, and Figure 19 The low-coordinate oxygen peak in (d) indicates the widespread existence of oxygen vacancies during the reconstruction process. 3+ The increase in the proportion of SO4 2- Adsorption occurs near Co sites, where surface coordination of oxygen anions enhances the Co 3+ In order to clarify the adsorption of SO4 2- We use the strong polarity of water molecules to promote SO4 2- Ethanol was used as a control.x Co 3-x O4-Ov-SO4 2- After the NCF samples were immersed in ethanol and deionized water for 12 hours, metal precipitation appeared in the samples immersed in water, resulting in lake blue and performance degradation. Figure 20 , while the sample immersed in ethanol showed no significant change. -2 In the initial stage of the IT test, the Co9S8-Ni3S2 / NCF sample showed enhanced performance as Figure 2 (g), while the performance of the Co9S8 / CF sample decreased rapidly, which was subsequently alleviated by the formation of Co3O4. The current density of both samples gradually decreased with decreasing electrolyte level; however, the Co9S8 / CF sample showed a faster decline, indicating that slow structural degradation is ongoing. Based on the existing evidence and previous studies, we conclude that the cobalt spinel oxide generated during the OER process contains a large number of oxygen vacancies. The presence of these vacancies has a positive effect on conductivity; however, they also destroy the periodicity and lead to structural instability. SO4 2- The adsorption of can stabilize oxygen vacancies and intermediates simultaneously, thereby reducing the energy barrier and enhancing the catalytic activity and stability of the reconstructed phase.

[0068] Therefore, the present invention adopts a kind of above-mentioned structure to self-reconstruct Co9S8-Ni3S2 / NCF into Ni x Co 3-x O4-Ov-SO4 2- / NCF to simultaneously enhance the oxygen evolution reaction activity and stability, using the self-reconstruction strategy of Co9S8-Ni3S2 / NCF to prepare partially nickel-doped cobalt spinel (Ni x Co 3-x O4-Ov-SO4 2- ), which can enhance the leaching of SO4 from the initial phase compared to cobalt spinel 2- The adsorption capacity was improved to achieve an overall water splitting time of more than 600 h at a current density of 1000 mA cm -2 , and has excellent activity. Co9S8-Ni3S2 / NCF is transformed into SO4 2- Adsorbed nickel-doped SO4 2- Cobalt spinel, at 1000mA cm -2 Under these conditions, the oxygen evolution reaction (OER) stability of 1000 hours was achieved. In situ Raman spectroscopy and XPS results showed that the partial substitution of nickel atoms for cobalt atoms enhanced the SO4 2- The adsorption capacity is improved, thereby promoting the formation of high-density active sites and accelerating the interfacial electron transfer at high current density.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A Co9S8-Ni3S2 / NCF self-reconstructed into Ni x Co 3-x O4-Ov-SO4 2- / NCF method for enhancing the activity and stability of oxygen evolution reaction, characterized in that The process includes the following: To synthesize Co9S8-Ni3S2 / NCF needle-shaped nanochains, NCF was reacted with 78 mg of sulfur powder at 160°C for 6 hours via a hydrothermal reaction in a solution that also included ammonium fluoride and urea. The mass ratio of cobalt to nickel in the NCF was 5.72:

1. The synthesized Co9S8-Ni3S2 / NCF was used as the anode and cathode in a 1 M KOH electrolytic cell at 1000 mA / cm 2 Under this condition, the anode is reconstructed to obtain Ni x Co 3-x O4-Ov-SO4 2- / NCF.

2. According to claim 1, a Co9S8-Ni3S2 / NCF self-reconstructs into Ni x Co 3-x O4-Ov-SO4 2- / NCF method for enhancing the activity and stability of oxygen evolution reaction, characterized by: Ni x Co 3-x O4-Ov-SO4 2- The mapping and EDS of / NCF show that the Co, Ni, S and O elements are evenly distributed on the surface of the reconstructed species.

3. The Co9S8-Ni3S2 / NCF self-reconstructs into Ni according to claim 1 x Co 3-x O4-Ov-SO4 2- / NCF method for enhancing the activity and stability of oxygen evolution reaction, characterized by: During the reconstruction process, Ni 3+ Replaces some of the Co in the octahedral vacancies 3+ , forming a normal spinel structure, and a large amount of sulfur elements are leached during the phase change process, and these elements are oxidized to SO4 2- and adsorbed on Ni x Co 3-x O4-Ov surface.

4. The Co9S8-Ni3S2 / NCF self-reconstructed into Ni according to claim 1 x Co 3-x O4-Ov-SO4 2- / NCF method for enhancing the activity and stability of oxygen evolution reaction, characterized by: Reconstructed Ni x Co 3-x O4-Ov-SO4 2- No secondary transformations were experienced during the long-term high current density OER process.

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